1. Field of the Invention
The present invention relates to apparatus for direct visualization of body passages and, in particular, to a catheter structure which allows an angioscope to be centered within a blood vessel during visualization while maintaining blood flow.
2. Discussion of the Prior Art
Optical scopes have been in use for some time for direct visualization of body passages. For example, endoscopes are used for viewing the gastrointestinal tract, bronchoscopes are used for viewing bronchial passages and arthroscopes are used for joint examination. These scopes are attached to a video camera which displays the image on a video monitor or, alternatively, the body passage is viewed directly through the eyepiece of the scope.
An angioscope is used for visualization in both the arterial and the venous systems. Typically, the angioscope is inserted into the artery or vein through an incision and then periodically advanced to obtain visualization at desired locations along a length o the vessel.
Angioscopy is a particularly difficult procedure in the arterial system. The pressure and the flow rate of blood are much higher in the arteries than in the veins, making it difficult to obtain the bloodless field required for the desired quality of visualization.
Typically, an angioscope is combined with a catheter which is used to introduce a bolus of sterile saline solution into the vessel at the distal end of the angioscope to provide a clear viewing field. However, particularly in the arterial system, if only a small amount of saline is used, the blood washes the saline flush away too quickly to allow visual examination. On the other hand, if a larger amount of flush solution is used, over a time period sufficient to allow adequate visualization, complications will arise. First, fluid overload of the patient will occur, causing electrolyte imbalance or congestive heart failure. Second, there will be a lack of perfusion to the tissue supplied by the artery undergoing angioscopy because the flush solution has cleared away the oxygen-carrying blood. This problem is particularly difficult in angioscopic evaluation of the coronary arteries, since cardiac muscle cannot tolerate prolonged ischemia. Balloon occlusion may be used, but it too may cause ischemia.
An additional major problem that is encountered in conventional angioscopy is that, during visualization, particularly in curved sections of the vessel, the angioscope lies against the wall of the vessel, obstructing the view. Balloon catheters have been used for centering the angioscope. However, as stated above, inflation of the balloon occludes the vessel. In addition, centering catheters that use balloons require an additional catheter lumen to inflate the balloon. This extra lumen either decreases the size of the irrigating lumen or increases the size of the centering catheter.